Edit: I decided I'd better sharpen up after buying my old Skoda Fabia in 2003 (my first buy from a dealer) and paying the price on the screen. Afterwards I realised that I'd been well and truly done and decided it wasn't going to happen again.
not all dealers are out to get you though, there is such a thing as a fair price and it's not always the case that a car needs to be knocked down dramatically. remember, a dealer worth their salt will obviously be in it for profit but if one does their homework, one will know if one is paying over the odds and walk away. if a car is priced fairly, as good as it would be to get a bit more knocked off, it's not a deal breaker if they wont imo. a free service and mot is always a nice extra though.
also, most cars are sold with a 3 month warranty with option to extend. i don't have a great deal of faith in aftermarket warranties and would feel a lot more confident going back to a dealer who i hadn't knocked down massively on price and taken out no extended warranty should there be a problem 6 months down the line.